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Wed, 19 Aug 2026 18:22:41 +0000 (GMT) Received: from [9.124.213.40] (unknown [9.124.213.40]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 19 Aug 2026 18:22:41 +0000 (GMT) Message-ID: Date: Wed, 19 Aug 2026 23:52:40 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] sched/topology: Add a cpus_read_lock to rebuild_sched_domains() From: Shrikanth Hegde To: Sebastian Andrzej Siewior , linux-kernel@vger.kernel.org Cc: Ben Segall , Dietmar Eggemann , Ingo Molnar , Juri Lelli , K Prateek Nayak , Mel Gorman , Peter Zijlstra , Steven Rostedt , Tim Chen , Valentin Schneider , Vincent Guittot , "chen.yu@linux.dev" , "Chen, Yu C" References: <20260813073855.ji2UrtVh@linutronix.de> <3a199af0-a7dd-4ca6-a4ae-3c53fe9bfec7@linux.ibm.com> Content-Language: en-US In-Reply-To: <3a199af0-a7dd-4ca6-a4ae-3c53fe9bfec7@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=CpuPtH4D c=1 sm=1 tr=0 ts=6a85f47a cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=P2gtcWylOtqNJfPpLFQA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: r7aBB3sgw8g-traqRTXrvAlnXn7CWhsB X-Proofpoint-GUID: ZZWe-oMOVkV0aB3N3IvBW0fI0ABAGmu0 X-Proofpoint-Spam-Info: AW1haW4tMjYwODE5MDE0MCBTYWx0ZWRfX60AX61zr1peP gPFY+OzqpTy8pTj6WAmnPxb2Z0e7wUvtJuviTJ/IB1O3OLQBckb3HlZUYOza+Mdhw/raGt2CsRj 3JmvBxj8KPtsNbxdWfaGnnULPOu/rFU= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE5MDE0MCBTYWx0ZWRfX38OZgs7RqUsP ECfn8BENw85SVO3XZ4tCbNwW9J6doyhYsOfYEhI/DABomEAOUPgPieguW73aEDVMW+QQuiUZl1B AJSMrzHO2Ly7pOWoMa9vNCMROf/FqdLHY2CaIcJrKGk61jRGXh8daUbzoWXFjZ+vwnLUP2eza+j l/RzohCRoPzds4Rf3ojyjW39ncQqaxTtn3Wi6q9UUxlQhYG5zdVyNzGEM7VVojjlVmGaQcv/KNW g9GeC5563ujjM7iXC33pmLXSCHiWsaHd46ylD0agZNvwvFPlqvklA/AG/U7cctN1C0L2bq0zyjp w/AYElU+Oib+ZAXflE9k+mxYd+bDacte76IpFjXuzSR17PfXFHDYMnkohFmGWObBsyoUXuEQnrc RN1jMiOy3TdCVo9TqH+EBOzXM2FJWVlSomwvXWENLgUOHpC42+JhK6HzVha2LtgHuzkhJ7VfDIl voIQ/R1HgeSzAjYvIkQ== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-19_05,2026-08-19_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0 bulkscore=0 malwarescore=0 phishscore=0 lowpriorityscore=0 spamscore=0 clxscore=1015 priorityscore=1501 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608190140 On 8/19/26 11:24 PM, Shrikanth Hegde wrote: > Hi Sebastian. > > On 8/13/26 1:08 PM, Sebastian Andrzej Siewior wrote: >> A read from /proc/sys/kernel/sched_rt_runtime_us leads to backtrace due >> to missing cpu_hotplug_lock with CONFIG_CPUSETS=n. The callchain is >> sched_rt_handler() -> partition_sched_domains() -> sched_cache_set() -> >> static_key_enable_cpuslocked(&sched_cache_present). >> >> sched_cache_set() itself is also invoked from sched_init_domains() which >> is early during the boot, holding just the sched_domains_mutex_lock(). >> Here is no warning because it happens before user space is running (and >> hotplug operations are not possible). >> >> There is also sched_cache_active_set() which acquires the hotplug lock >> before invoking any of the _cpuslocked() functions. >> >> This is only a problem with CONFIG_CPUSETS=n because in the =y case the >> other implementation of rebuild_sched_domains acquires the CPU-hotplug >> lock. >> >> Acquire CPU hotplug lock before in rebuild_sched_domains(), before >> partition_sched_domains() is invoked for the CONFIG_CPUSETS=n case. >> >> Fixes: a7660ce1590fc ("sched/cache: Fix has_multi_llcs iff at least one partition has multiple LLCs") >> Signed-off-by: Sebastian Andrzej Siewior >> --- >> v1…v2: https://lore.kernel.org/all/20260812095800.gl06ANul@linutronix.de/ >>    - Move the lock from partition_sched_domains() to >>      rebuild_sched_domains() in the CONFIG_CPUSETS=n since this is the >>      only affected case. Noticed by Yu C Chen and Tim Chen. >> >>   include/linux/cpuset.h | 1 + >>   1 file changed, 1 insertion(+) >> >> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h >> index 65d76a38974ba..bf3999daa080a 100644 >> --- a/include/linux/cpuset.h >> +++ b/include/linux/cpuset.h >> @@ -273,6 +273,7 @@ static inline void dl_rebuild_rd_accounting(void) >>   static inline void rebuild_sched_domains(void) >>   { >> +    guard(cpus_read_lock)(); >>       partition_sched_domains(1, NULL, NULL); >>   } > > Now, both rebuild_sched_domains have the same code. I guess it is worth > moving it out of CONFIG_CPUSETS. > Ignore my comments. I clearly need to get rest. > kernel/cgroup/cpuset.c: > void rebuild_sched_domains(void) > { >         cpus_read_lock(); >         rebuild_sched_domains_cpuslocked(); >         cpus_read_unlock(); > } > Sorry for the noise. Looks good to me. Reviewed-by: Shrikanth Hegde